As a conventional example of thermal flow meters, the thermal flow rate sensor described in Japanese Patent Application Laid-Open No. 2011-237456 is known. In this example, a bridge circuit that detects heater temperature is provided with a balance adjusting resistor. The potential across the balance adjusting resistor is taken out and this end-to-end potential is received by resistors connected in series in multiple stages. An intermediate potential produced between a resistor and a resistor connected in series in multiple stages can be adjusted by changing the intermediate potential with a switch before taking it out. Even when the resistance value of a resistive element configuring the bridge circuit, the balance of the bridge circuit can be adjusted.
In the break detection circuit of a bridge circuit described in Japanese Patent Application Laid-open No. 2012-008014, a first series circuit made up of two resistors and a second series resistance made up of two resistors are connected in parallel to form a bridge circuit. A wire connects a first output terminal for taking out an intermediate potential of the first series circuit with an amplifier; and another wire connects a second output terminal for taking out an intermediate potential of the second series circuit with an amplifier. These wires are respectively connected, to the ground potential through a resistor. When a break occurs in the first output terminal, the first output terminal is brought to the ground potential. When a break occurs in the second output terminal, the second output terminal is brought to the ground potential. Thus a break of the first output terminal and the second output terminal can be detected.